ACTB and atypical Rett syndrome: Of note, both promoters used in this study were already used in clinical settings: the Chicken β-Actin promoter (CBA) [20, 28] and the truncated methyl-CpG-binding protein 2 (MeCP2) promoter (P546) [29], that has been proved to assure long lasting and physiological transgene expression in Rett syndrome [27] and in Batten disease preclinical models [26].